What are Weld Defects?
In short, a weld defect is any flaw or imperfection that compromises the intended use of a weldment.
This also implies a flaw or imperfection may not compromise the weld, and a weld is said to have a discontinuity when this occurs. So, a weld can have a discontinuity and not be considered defective.
Common Weld Defects and Discontinuities
1. Cracks
We may as well start with one of the most obvious and serious defects in a weld – cracks. These weaken a weld, and even worse, cracks tend to grow at a rapid rate making the problem worse.
So, it goes without saying you do not want any cracks in your welds. But it can be a challenge, and there are three main types of cracks:
- Longitudinal cracks run along, or are parallel, to the length of the weld.
- Transverse cracks run across the width of a bead.
- Crater cracks usually occur at the end of a weld when the arc is terminated. They are often star-shaped and form when a dent or “crater” is formed at the end of a weld.
Cracks can further be categorized as hot or cold cracks.
Welds can be heated to over 10,000°C, and hot cracks occur as the weld cools and transitions from the liquid to the solid phase. Hot cracks tend to occur when the wrong alloy filler material is used.
Cold cracks occur after the weld has cooled. They can occur hours or days after the joint is made. This defect usually occurs when welding steel and is often caused by deformities in the base metal.
2. Inclusions
Impurities can become trapped inside a weld, and these are referred to as inclusions. Contaminants trapped inside a weld dramatically weaken the joint.
Slag often forms when flux is used, such as brazing and stick, flux-cored, and submerged arc welding. The slag must be allowed to float to the top of the puddle and not become trapped inside the bead. That means the molten pool should not be allowed to cool too fast.
But it can occur with MIG welding as well. Bits of rust and even tungsten can be counted as slag and can cause contamination in your welds. So, MIG and TIG welding is not immune to inclusions.
3. Lack Of Fusion
It may seem obvious, but the filler material must be well bonded to the base metal on both sides and to welds underneath during multiple passes.
If there are voids, gaps, or poor adhesion, the joint will be structurally impaired.
4. Porosity
Weld porosity (also known as wormhole weld) is where gas bubbles accumulate and get trapped inside a weld. This is also said to be porous. A cross-section of a porous weld bead will resemble a sponge with all the air bubbles trapped inside.
As you weld, gases like steam, hydrogen, and carbon dioxide can be generated, and they normally bubble out of the molten bead. But if the gas bubbles are trapped, they can weaken your joint, and the work is ruined.
5. Undercut
When the welding process results in spots or sections being less than the original base metal, the defect is referred to as an undercut. This will often appear as a “notch” at the edge of a weld, either on the top or bottom of the weld.
A loss in thickness reduces the strength of the weldment and makes the joint susceptible to fatigue. This defect is often the result of too high a current or moving too fast.
6. Poor Penetration
When the bead does not fill a butt joint all the way to the bottom, the weld achieves poor penetration. It is also referred to sometimes as incomplete penetration. Whatever you call it, this form of defect also compromises the integrity of a joint.
7. Burn Through
If too much heat is applied during the weld, you can actually blow a hole through the metal. This defect is referred to as burn through, but sometimes it is also called melt through. Creating a hole defeats the purpose of a weld and destroys the joint.
This type of defect is usually encountered with thin stock, material les
7. Burn Through
If too much heat is applied during the weld, you can actually blow a hole through the metal. This defect is referred to as burn through, but sometimes it is also called melt through. Creating a hole defeats the purpose of a weld and destroys the joint.
This type of defect is usually encountered with thin stock, material less than 1/4 inch thick. But it can occur with thicker stock if your welder settings are too high, if the gap between pieces is large, and/or you are moving the torch too slow.
8. Under-Fill
When the weld bead sits below the surface of the base metal, the weld is said to be under-filled. The bead itself is thinner than the base metal, which weakens the joint. This condition often appears as a “rut” that runs the length of the bead and is sometimes called a convex joint.
9. Excess Reinforcement
In contrast to an underfilled joint, a defect results when there is too much filler material in the joint. This is known as excess reinforcement or a “high” crown. Project specifications and codes often regulate what is considered too high.
At times, excess reinforcement may even come out the bottom of the joint. Th
9. Excess Reinforcement
In contrast to an underfilled joint, a defect results when there is too much filler material in the joint. This is known as excess reinforcement or a “high” crown. Project specifications and codes often regulate what is considered too high.
At times, excess reinforcement may even come out the bottom of the joint. This is sometimes referred to as excess penetration.
Other variations of the defect include narrow, steep-sided beads caused by an insufficient coating of flux on your feed wire or low voltage.
Avoiding Defects and Discontinuities
As you can see from this shortened list of common defects (yes, there are actually more we could have discussed), there are good reasons why having a Callahan Weld Inspection LLC professional welding inspector there every step of the way during the welding process.
Defects usually occur when one of these basics is not followed. The following in conjunction with a CWI weld inspector can help avoid rejected/ unacceptable welds:
- Prepare the base metal to ensure it is clean and contaminant-free
- Position the pieces correctly for the type of weld to be performed with no large gaps
- Create V grooves at the proper angle when needed
- Set both the amperage and the voltage correctly in accordance with approved WPS
- Maintain a proper arc length
- Move the torch at an optimum speed
- Use a correctly sized electrode/ consumable
- Ensure your feed wire is not impeded
- Find and keep the right welding angle
- Properly weave when necessary
- Avoid mechanical damage to the parent metal and finished bead
Knowing how to identify the various defects and correct them makes your joints stronger and more presentable. For this I recommend hiring Callahan Weld Inspection LLC to ensure a professional welding inspector is making sure all of these guidelines are being followed.
All these potential defects may seem overwhelming and impossible to avoid at first. Having a weld inspector present during welding operations helps in keeping unacceptable welds from happening potentially saving hours in repair time and costs.